1. Field of the Invention
The invention relates to shoe covers, such as for use in a medical field, such as in an operating room, and to methods for their production. More particularly, the invention relates to shoe covers made of a dipped elastomer and to a dipping process therefor employing a narrow profile form.
2. Background Information
Typically, shoe covers for use in a sterile operating room are formed of a loose fitting cloth or plastic, such as thin polyethylene sheet material or nonwoven fabric which is sewn into a foot shaped configuration. To protect the wearer against seepage of blood through a nonwoven material, such covers may incorporate a layer of fluid impervious material, such as a thermoplastic. Production of such shoe covers requires a complex sewing operation and sewing machinery. Further, as shoe covers of this type are loose fitting they may breathe as the wearer moves causing dust to move in and out of the shoe cover, potentially creating a source of contamination. A, tight fitting elastomeric cover, such as may be formed in a dipping process, provides a low cost alternative and alleviates the problem of breathing.
Typically, dipped elastomeric items are produced by a process which involves dipping a bulky porcelain or aluminum form into a solution of coagulant (usually a solution of calcium nitrate in water or alcohol), drying the coagulant and then immersing the form into a latex compound and dwelling for a specific duration. After depositing the desired thickness of latex film on the form, the form is withdrawn from the latex compound and usually rotated throughout the period of time for completion of gelling the latex film. After the film is gelled, it is leached with water to remove any water soluble materials from the deposit, it is dried, vulcanized and stripped from the form as a finished product.
The Abramson U.S. Pat. No. 4,103,439 discloses a shoe cover of the type formed of rubber with a black dispersion suitable for protecting ones shoes in inclement weather and commonly referred to as "rubbers." Abrahamson also indicates that such shoe covers could be employed in industrial clean rooms and the like to assist in maintaining a dust free environment. The form used by Abrahamson is a three dimensional representation of a human foot inside of a shoe.
It has been found that elastomers age best in the static state, that is to say, all other factors being equal, a latex rubber article will age better without being stressed or distorted. Shoe covers formed of the presently available three dimensional forms exhibit folding lines and sharp creases during storage and shipping which can crack and generally degrade when exposed to the deleterious effects of oxygen, ozone or ultra-violet radiation, or to any combinations of these. Consequently, it is desirable to avoid any such sharp creases in the finished shoe cover product if at all possible.
The relatively large surface areas on the three dimensional forms that lie parallel to the liquid surface tend to trap air during dipping causing voids or blisters in the film. Some dipping operations, such as disclosed by Abramson '439, provide a tilting mechanism for tilting the form as it enters the liquid. Of, course this adds complexity to the dipping operations.
Nearly twenty years ago, the Stockum U.S. Pat. No. 4,047,251, issued on Sep. 13, 1977 and incorporated herein by reference, disclosed a flat form useful for producing elastomeric gloves. Compared to conventional three dimensional glove forms, it was cheaper to produce the form, allowed more gloves to be produced in a single dipping operation and solved several other technical problems in the art of glove dipping. However, such technology has apparently not heretofore migrated to the production of shoe covers. The human hand is relatively flat and a flat form for the production of gloves mimics the shape of the human hand fairly acurately. Human feet, especially when shod, have a substantial lateral dimension such that they are not considered flat. Accordingly, it is not obvious that a flat form would produce an acceptable shoe cover.
Further, in protecting medical workers, shoe covers are routinely formed of non-woven fabrics, sometines incorporating a liquid impervious nonelastic inner layer.